Bottom Line:
Parasitological data were obtained through repeated cross-sectional surveys that were carried out during 1997-2010 in Anhui Province, East China.The POPs associated with these oscillatory components showed that the pattern near the Yangtze River varied markedly and that the disease risk appeared to evolve in a Southwest/Northeast orientation.The POP coefficients showed decreasing tendency until 2001, then increasing during 2002-2005 and decaying afterwards.

Affiliation: Department of Epidemiology, School of Public Health, Fudan University, Shanghai, China; Key Laboratory of Public Health Safety, Ministry of Education, Shanghai, China; Laboratory for Spatial Analysis and Modeling, School of Public Health, Fudan University, Shanghai, China.

ABSTRACT

Background: The Chinese national surveillance system showed that the risk of Schistosoma japonicum infection fluctuated temporally. This dynamical change might indicate periodicity of the disease, and its understanding could significantly improve targeted interventions to reduce the burden of schistosomiasis. The goal of this study was to investigate how the schistosomiasis risk varied temporally and spatially in recent years.

Methodology/principal findings: Parasitological data were obtained through repeated cross-sectional surveys that were carried out during 1997-2010 in Anhui Province, East China. A multivariate autoregressive model, combined with principal oscillation pattern (POP) analysis, was used to evaluate the spatio-temporal variation of schistosomiasis risk. Results showed that the temporal changes of schistosomiasis risk in the study area could be decomposed into two sustained damped oscillatory modes with estimated period of approximately 2.5 years. The POPs associated with these oscillatory components showed that the pattern near the Yangtze River varied markedly and that the disease risk appeared to evolve in a Southwest/Northeast orientation. The POP coefficients showed decreasing tendency until 2001, then increasing during 2002-2005 and decaying afterwards.

Conclusion: The POP analysis characterized the variations of schistosomiasis risk over space and time and demonstrated that the disease mainly varied temporally along the Yangtze River. The schistosomiasis risk declined periodically with a temporal fluctuation. Whether it resulted from previous national control strategies on schistosomiasis needs further investigations.

pntd.0003715.g001: Endemic area of schistosomiasis japonica in Anhui Province, People’s Republic of China.The river in the north is the Huaihe River and the one in the south is the Yangtze River. The map was created using ArcGIS software (version 10.0, ESRI Inc. Redlands, CA).

Mentions:
The S. japonicum infection prevalence data were collected from repeated cross-sectional surveys carried out by the health professionals of the Anhui Institute of Parasitic Diseases annually between 1997 and 2010. These data were originally collected through village-based field surveys using a two-pronged diagnostic approach (all residents aged 5 to 65 years were screened by a serological test and then confirmed by a fecal parasitological test (Kato-Katz technique)) [16], with aggregated data available to us at the county level. For our spatio-temporal variation analysis, we removed the counties with zero prevalence of the disease during the study period and 31 schistosome-endemic counties were included in this study (Fig 1).

pntd.0003715.g001: Endemic area of schistosomiasis japonica in Anhui Province, People’s Republic of China.The river in the north is the Huaihe River and the one in the south is the Yangtze River. The map was created using ArcGIS software (version 10.0, ESRI Inc. Redlands, CA).

Mentions:
The S. japonicum infection prevalence data were collected from repeated cross-sectional surveys carried out by the health professionals of the Anhui Institute of Parasitic Diseases annually between 1997 and 2010. These data were originally collected through village-based field surveys using a two-pronged diagnostic approach (all residents aged 5 to 65 years were screened by a serological test and then confirmed by a fecal parasitological test (Kato-Katz technique)) [16], with aggregated data available to us at the county level. For our spatio-temporal variation analysis, we removed the counties with zero prevalence of the disease during the study period and 31 schistosome-endemic counties were included in this study (Fig 1).

Bottom Line:
Parasitological data were obtained through repeated cross-sectional surveys that were carried out during 1997-2010 in Anhui Province, East China.The POPs associated with these oscillatory components showed that the pattern near the Yangtze River varied markedly and that the disease risk appeared to evolve in a Southwest/Northeast orientation.The POP coefficients showed decreasing tendency until 2001, then increasing during 2002-2005 and decaying afterwards.

Affiliation:
Department of Epidemiology, School of Public Health, Fudan University, Shanghai, China; Key Laboratory of Public Health Safety, Ministry of Education, Shanghai, China; Laboratory for Spatial Analysis and Modeling, School of Public Health, Fudan University, Shanghai, China.

ABSTRACT

Background: The Chinese national surveillance system showed that the risk of Schistosoma japonicum infection fluctuated temporally. This dynamical change might indicate periodicity of the disease, and its understanding could significantly improve targeted interventions to reduce the burden of schistosomiasis. The goal of this study was to investigate how the schistosomiasis risk varied temporally and spatially in recent years.

Methodology/principal findings: Parasitological data were obtained through repeated cross-sectional surveys that were carried out during 1997-2010 in Anhui Province, East China. A multivariate autoregressive model, combined with principal oscillation pattern (POP) analysis, was used to evaluate the spatio-temporal variation of schistosomiasis risk. Results showed that the temporal changes of schistosomiasis risk in the study area could be decomposed into two sustained damped oscillatory modes with estimated period of approximately 2.5 years. The POPs associated with these oscillatory components showed that the pattern near the Yangtze River varied markedly and that the disease risk appeared to evolve in a Southwest/Northeast orientation. The POP coefficients showed decreasing tendency until 2001, then increasing during 2002-2005 and decaying afterwards.

Conclusion: The POP analysis characterized the variations of schistosomiasis risk over space and time and demonstrated that the disease mainly varied temporally along the Yangtze River. The schistosomiasis risk declined periodically with a temporal fluctuation. Whether it resulted from previous national control strategies on schistosomiasis needs further investigations.